DBD-like He-plasma jet: Pure helium (Alphagaz, 5.0) is transported with a gas flow of 500 sccm through a quartz capillary with an inner diameter of 1 mm and a wall thickness of 0.25 mm. A high-voltage electrode (a coiled copper wire) is placed around the quartz tube at a distance of 20 mm from the open end of the capillary. The high-voltage pulse sequences have a repetition frequency of 4 kHz and a sequence duration of 10 μs. Each sequence consists of high-voltage pulses (up to about 20 kV) with a frequency of about 700 kHz and a damped amplitude. PEO microdischarge ignitions: A cylindrical, double-walled borosilicate vessel is used as electrolytic cell. Two opposite, optical-grade, quartz glass windows with a diameter of 40 mm ensure light transmission down to λ = 200 nm. A stainless steel cylinder with a diameter of 4 mm is used as cathode. The substrates for the PEO process are aluminium AW-6061 plates with a dimension of 20 mm × 20 mm × 2 mm, as well. These substrates serve as anode during the process. This first anodisation phase is imitated by a high voltage anodisation treatment of 3 min at a direct current (DC) voltage of 250 V and current density related to the anode surface of approximately 0.125 A/cm^2. To ensure, that no breakdown appears, the voltage 250 V is chosen, which is roughly in the middle between the typical maximum of anodisation voltages at around 80 V and the breakdown voltage of the PEO process at around 470–480 V in this setup.